Method of oxidizing benzene to maleic anhydride using a vanadium, molybdenum, boron containing catalyst

ABSTRACT

A catalyst useful for the oxidation of organic compounds, particularly the partial oxidation of benzene with molecular oxygen to produce maleic anhydride, comprises the oxides of molybdenum and vanadium and a minor amount of boron. A preferred form of the catalyst further includes phosphorus and at least one member of the group consisting of cobalt, nickel and iron, and sodium.

United States Patent [1 1 Barker Feb. 18, 1975 4] METHOD OF OXIDIZINGBENZENE TO 2,777,860 1/1957 Egbert 260/3468 MALEIC ANHYDRIDE USING A3,535,346 10/1970 Sudo et al 260/3468 VANADIUM, MOLYBDENUM, BORONCONTAINING CATALYST Robert S. Barker, Little Ferry, N.J.

Halcon International, Inc., New York, NY.

Filed: Dec. 27, 1972 Appl. No.: 318,941

Related U.S. Application Data Division of Ser. No. 76,249, Sept. 28,1970, Pat. No. 3,759,840.

Inventor:

Assignee:

U.S. Cl 260/3463 A Int. Cl. C07c 57/14 Field of Search 260/3468 A OTHERPUBLICATIONS Vaidyanathan, Chemical Age of India (1968), Vol. 19, (No. 5pp. 363-69.

Primary Examiner-I-Icnry R. Jiles Assistant Examiner-Bernard I. DentzAttorney, Agent, or Firm-William C. Long; David Dick; Riggs T. StewartABSTRACT 4 Claims, N0 Drawings 1 METHOD OF OXIDIZING BENZENE TO MALEICANHYDRIDE USING A VANADIUM, MOLYBDENUM, BORON CONTAINING CATALYST Thisis a division, of'application- Ser. No. 76,249 filed Sept. 28, 1970 nowUS. Pat. No. 3,759,840.

This invention relates to catalysts and is more particularly concernedwith catalysts which are useful in the oxidation of organic compounds,especially the partial oxidation of benzene with molecular oxygen toproduce maleic anhydride. The invention is also con cerned with the useof such catalysts in oxidations of this character.

The preparation of maleic anhydride by the selective partial oxidationof benzene in a vapor phase system using a contact catalyst involves awell-known reaction and has been practiced commercially for many years.Among catalysts which have been found useful and effective commerciallyfor this purpose are those based upon a combination of vanadium andmolybdenum in oxidized form. In the development of improved catalysts ofthis nature the vanadium and molybdenum oxides have been combined withthe oxidized forms of one or more other metals of various types.

Known commerical catalysts of this character are effective and generallysatisfactory, but in the field of catalysis there is always a continuingsearch for improved catalyst compositions, and a particular objective isthe discovery of means for increasing the activity of the catalystswhile at the same time enhancing, or at least maintaining, theselectivity of the catalyst in favor of the desired product. Ofparticular interestto persons skilled in this art is the development ofmeans for increasing or prolonging the active life of the catalyst.There are obvious important practical benefits in a catalyst which isactive and retains its activity for a long period of time before itneeds to be replaced.

It is accordingly an object of this invention to provide an v improvedcatalyst of the vanadium oxidemolybdenum oxide type which has anincreased active life.

It is a further objective of the invention to provide a catalyst of thecharacter indicated which has desirable activityand selectivitycharacteristics.

It is a more specific object of the invention to provide a catalystwhich has an increased active life and has high activity and selectivitywith respect to the production of maleic anhydride by the partialoxidation of benzene.

Another object of the invention is to provide an improved method for thepartial catalytic oxidation of benzene to produce maleic anhydride whichemploys a catalyst of the type described.

In accordance with the invention it has been discovered that thecombination, in a catalyst of the vanadium oxide-molybdenum oxide type,of a small amount Improved results are observed even when boron is theonly additive in the vanadium oxide-molybdenum oxide catalyst system andthe active catalyst composition consists only of the vanadiumoxide-molybdenum oxide combination in addition to the boron value.However, from the standpoint of optimum benefits and catalysteffectiveness, it is preferred that the boron be used in vanadiumoxide-molybdenum oxide catalyst compositions of the type which containother components which have been found to enhance the activity ofcatalyst systems of this nature, as disclosed, for example, in Egbertand Becker U.S. Pat. No. 2,777,860 and Egbert US. Pat. No. 3,221,671.Thus, it is advantageous that the catalyst also contain phosphorus, andcobalt, iron or nickel, or mixtures thereof. In addition,

it is advantageous to have present a small amount of sodium and, asindicated above, the boron is suitably employed in making the catalystof the invention in the form of a sodium borate, so that the use of thiscompound will incorporate not only the essential boron value into thecomposition, but will also provide an effective quantity of sodium.

In the catalyst composition of the invention, all of the metalsmentioned are believed to be in the form ofoxides, e.g., V 0 M00 P 0 NaO, C0 0 Ni O Fe O and B 0 since the catalyst is advantageously preparedby means of known techniques which involve activation by aprolonged-heat treatment as a concluding step. However, it-is convenientto refer to the proportions of the various components in terms of themetal elements. In this way, the catalyst of the invention can becharacterized'by its analytical composition in which the components areexpressed in meaningful terms without regard to the exact-chemicalcomposition or form in which they may actually exist. Thus, basing theproportions on a molar quantity of vanadium as 1.0, the molybdenum maybe in the range of 0.1 to 0.95 mol, the phosphorus content may be in therange of 0.01 to 0.5 mol, the alkali metal content may be in the rangeof 0.02 to 0.6 mol, the content of the Co, Ni, or Fe may be in the rangeof 0.005 to 0.05, mol, and the boron may be in the range of 0.005 to 0.3mol. As is customary in the case of vanadium oxidemolybdenum oxideoxidation catalysts, the active catalytic components are supported upona suitable carrier, generally in the form of refractory inorganicparticles, of any of the various catalyst supports known to this art,conventionally characterized as inert, having a surface area of at most5 square meters per gram, e.g., 0.002 to 5 square meters per gram,preferably 0.005 to 3 square meters per gram, and ofa particle sizeadapted for the particular process in which the catalyst is to be used.Generally suitable are particles having an average diameter of about 1/5/2 inch, although larger or smaller particle sizes can also be employed,e.g. average diameters of /5 to inch.

} The weight of catalyst mixture relative to the support may be in therange of 1.0 to 20 percent, preferably about 10% based on the weight ofthe support. Although alumina is a preferred support, other refractorysupport materials may be used, such as silicon carbide, silica, titania,fullers earth, pumice, asbestos, kiesel- 'guhr, and the like.Thecarriermaterial may be in the form of pellets, lumps; granules,spheres, rings or other formed pieces, or in other forms which may be ofregular orirregular contour;

1t is appreciated that boron, generally in the form of a boronoxide, hasbeen used in catalysts for the partial oxidation of organic compounds tomaleic anhydride as disclosed, for example, in Hartig US. Pat. Nos.2,625,519 and 2,691,660. However, in such prior operations, the boronoxide has been used as an equivalent of, or as a substitute for, aphosphorus oxide or a vanadium oxide. In accordance with the presentinvention, in contrast, boron is used in addition to the vanadium oxideand the phosphorus oxide and in this environ ment, wherein the boron ispresent in a small amount in relation to vanadium, it exhibits thelife-prolonging, selectivity and activity-enhancing action previouslymentioned.

When the catalyst of this invention is used in the vapor-phase partialoxidation of benzene to form maleic anhydride, the oxidation conditionsemployed are those generally associated with this reaction, asdisclosed, for example, in US. Pat. Nos. 2,777,860 and 3,21 1,671.Typical conditions involve jacket temperatures of 340 to 420C, a ratioof benzene to molecular oxygen:l1.6 to (mol), and a space velocity of2,000 to 4,000 hour and pressures of atmospheric to 3 atm. Similarly,conventional reactors or converters can be employed and the processes inwhich the catalyst of the invention can be used are, therefore, notrestricted to particular conditions or types of apparatus. However, itis one of the features of the catalyst of this invention that thepartial oxidation of benzene to maleic anhydride can be carried out atlower temperatures than would norm ally be employed with a correspondingcatalyst having no boron content, all other conditions being the same.

As. mentioned, the catalyst is suitably prepared by more or lessconventional techniques. In a preferred procedure, for example, themolybdenum, in the form of ammonium molybdate, is dissolved inconcentrated aqueous HCl (35 percent) followed by the addition of boron,in the form of hydrated sodium tetraborate, as a solution in hot water.Ammonium metavanadate is dissolved in concentrated HCl and added to thefirst HCl solution with stirring. When a phosphorus value is to beincluded, it is added, e.g., as hdyrated disodium acid phosphate, as asolution in hot water to the firstnamed HCl solution, and when Co, Niand/or Fe are to be incorporated a water-soluble salt of the metal,e.g., cobalt nitrate hexahydrate, is dissolved in water and theresulting aqueous solution is added to the ammonium metavanadatesolution. The two HCl solutions are then mixed by slowly adding themolybdate solution to the metavanadate solution and the combinedsolution mixed with particles of a suitable refractory carrier andevaporated, resulting in the disposition of the salts on the surface andin the pores of the carrier. The coated carrier particles are thenactivated by calcining them in a kiln or oven, or in a tube throughwhich air is passed, at an elevated temperature (e.g. l75400C) for Va to2 hours. Since the preferred form of the catalyst of this invention isrelated to the catalyst disclosed in U'.-S. Pat. Nos. 2,777,860 and3,221,671, the catalyst preparation methods disclosed in those patents,with the further addition of the boron compound are suitably employed.

While, as mentioned; the invention in its broadest sense is not limitedto a particular carrier material, a support is preferred which has anapparent porosity (pore volume) of at least 35 percent, a surface area(square meters per gram) of about 0.01 to about 1, and

a major pore diameter range of 50 to 1,500 microhs, preferably at leastpercent of 50 to 1,500 micron size. An alumina support having thesecharacteristics is preferred, especially an alumina-silica supportcontaining up to about 20 percent silica, the balance beingsubstantially alumina. Particularly good results are obtained with asupport of the character indicated which has an apparent porosity of atleast 50 percent, and a pore diameter range of at least percent of 50-l,500 micron size.

The features of the invention will be more readily apparent from thefollowing specific examples of typical application. It will beunderstood, however, that these examples are for the purpose ofillustration only and are not to be interpreted as limiting theinvention.

EXAMPLE I A first solution is prepared by dissolving 103g. of ammoniummolybdate in 1,000 ml. of cone. hydrochloric acid, and then 8.6g. sodiumborate pentahydrate in 75 ml. hot'water (75C) is added to the solutionwith stirring, followed by addition of 10.5g. disodium acid phosphate inheptahydrate in 25 ml. hot water. A sec- 'ond solution is prepared bydissolving 167g. ammonium metavanadate slowly in 500 ml. of conc.hydrochloric acid followed by the addition of 8.8g. cobalt nitratehexahydrate in 25 ml. of water (25C). The first solution isthenslowlyadded to the second solution with stirring and the resultantbrown mixture poured over 1,500 ml. of 3-5 mesh aggregate pellets of acom-' mercial alumina catalyst carrier composed of about 85 percent A1 0about 13.5 percent SiO and very small amounts of other oxides asimpurities, primarily alkali metal oxides and alkaline earth metaloxides. This carthereby being converted into their oxides; In similarmanner, there are prepared a series of other catalysts, supported on thealumina carrier, each containing a combination of vanadium, molybdenum,phosphorus, sodium, nickel, cobalt or iron and boron within the scope ofthe formulation set forth above, but formed from varying quantities ofprecursor salts or employing different precursor salts.

In order to evaluate the foregoing catalysts, each is used to form acatalyst bed in a series of runs wherein benzene is partially oxidizedby means of molecular oxygen to .maleic anhydride. For this purpose,each catalyst is charged into a vertical reactor tube of 0.9 inchinternal diameter, to a bed height of inches, surrounded with atemperature regulating medium such as salt contained in a heatingjacket. A benzene-air mixture is fed downwardly through the reactor at alinear velocity of one foot per-second calculated at reactionconditions. The feed mixture contains 1.4 mol percent of benzene in air,and the jacket temperature is maintained in the range of 360 to 375C.The product is recovered in known manner. The results obtained with eachof the catalysts are shown in the following table wherein catalyst No. lis the catalyst prepared in the manner described at the beginning ofthis example.

Catalyst No. 2 is like catalyst No. 1, except that the amount ofammonium molybdate is increased to ll6g., and l5.lg. trisodium phosphate(Na;;PO .l2H O) and 114g. Na B .l0H O (sodium tetraborate) are usedinstead of disodium acid phosphate and sodium borate pentahydrate.Catalyst No. 3 is identical with catalyst No. 2, except that 8.8g nickclnitrate (Ni(NO;,) .6l-l O) is used instead of cobalt nitrate. CatalystNo. 4 is formed from l67g. ammonium vanadate, 106g. ammonium molybdate,l4.lg. disodium acid phosphate, 7.55 cobalt nitrate, 254g. nickelnitrate and 9.6g. sodium tetrahorate. Catalyst No. 5 is formed from1675;. ammonium vanadate, 128g. ammonium molybdate, l6.6 trisodiumphosphate, 10.31,. sodium tetraborate, 8.8g. nickel nitrate, and 4g.Fe(NO;,) Catalyst No. 6 is the same as catalyst No. 2 except that 102g.Na H- PO .7H O is used instead of trisodium phosphate. Catalyst No. 7 isalso like catalyst No. l but is formed from 455g. 85 percent phosphoricacid instead of disodium acid phosphate and also from 304g. NaCl.

an analogous catalyst which is free from boron in the actual vapor-phasepartial oxidation of benzene to maleic anhydride in an acceleratedtesting system in which the effect of several months of operation can bereduced to a matter of hours. In the accelerated test, the operatingconditions observed correspond to those described in Example I. exceptthat a temperature of 440C is used, but the temperature is reduced to370C at repeated intervals to measure the activity (conver sion) at thelatter temperature.

Using this accelerated method, it is found that in a typical case, acatalyst containing boron in accordance with this invention, e.g..corresponding to catalyst No. 4 described above, exhibits asignificantly increased active life in comparison with an analogouscatalyst having no boron content.

The embodiments of the invention in which an exclusive property isclaimed are defined as follows:

1. A process for the preparation of maleic anhydride TABLE I 1 CatalystTemperature, C Selectivity. Mol /1 Conversion. Wt.'71 Yield. Wtf/zWhile, as mentioned, the introduction of a boron value into a vanadiumoxide-molybdenum oxide cata lyst system is of particular interest from acommercial standpoint when the catalyst system also contains phosporus,sodium and cobalt, nickel or iron values, the effect of the boron valuecan be observed in the case of this class of catalyst in which onlyvanadium oxide and molybdenum oxide are present in addition to the boronvalue or in which only one ofthe above mentioned additional additives isadded to the combination. This is demonstrated by the followingexperiments in which the procedure described in example I is used toprepare a catalyst A from l67g. ammonium vanadate and 128g. ammoniummolybdate, a catalyst B from 167g. ammonium vanadate and 106g. ammoniummolybdate and 1 1.4g. Na B O .l0l-l O, a catalyst C from 167g. ammoniumvanadate, 106g. ammonium molybdate and 7.6g. Na PO,.l2l-l O, and acatalyst D employing the same precursors as in catalyst C but, inaddition, including 1 l.4g. Na- BJ,O .l0H O. When these catalysts areevalu ated in the preparation of maleic anhydride from benzene inaccordance with the procedure described above, the following results areobtained:

which comprises oxidizing benzene in the vapor-phase with molecularoxygen in the presence of a catalyst consisting essentially of oxides ofvanadium, molybdenum and boron, and an oxide of at least one member ofthe group consisting of phosphorus, cobalt, nickel, iron and sodium, therelative amounts of said oxides, expressed as V, Mo, B, P, Co, Ni, Feand Na being, per mol of V, 0.1 to 0.95 mol Mo, 0.005 to 0.3 mol B, upto 0.5 mol P, up to 0.05 mol Co, up to 0.05 mol Ni, up to 0.05 mol Feand up to 0.6 mol Na.

2. A process as defined in claim 1, wherein said catalyst contains 0.0]to 0.5 mol phosphorus.

3. A process as defined in claim 2, wherein said catalyst contains 0.02to 0.6 mol sodium and 0.005 to 0.05 mol of at least one member of thegroup consisting of cobalt, nickel and iron.

4. ln the vapor-phase oxidation of benzene to maleic anhydride withmolecular oxygen the improvement which comprises effecting suchoxidation in the presence of a molybdenum oxide-vanadium oxidephosphorus oxide catalyst wherein said molybdenum oxide, vanadium oxide andphosphorus oxide, expressed as Mo, V and P, are present per mol of V inthe amount As pointed out above, one of the characteristics of thecatalyst of this invention is prolonged active life. This is clearlydemonstrated by comparing a typical catalyst in accordance with theinvention which is characterized by a small but effective content ofboron with of 0.1 to 0.95 mol Mo and 0.01 to 0.5 mol P, in combinationwith a small amount of boron oxide effective to prolong the active lifeof said catalyst.

1. A PROCESS FOR THE PREPARATION OF MALEIC ANHYDRIDE WHICH COMPRISESOXIDIZING BENZENE IN THE VAPOR-PHASE WITH MOLECULAR OXYGEN IN THEPRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF OXIDES OF VANADIUM,MOLYBDENUM AND BORON, AND AN OXIDE OF AT LEAST ONE MEMBER OF THE GROUPCONSISTING OF PHOSPHORUS, COBALT, NICKEL, IRON AND SODIUM, THE RELATIVEAMOUNTS OF SAID OXIDES, EXPRESSED AS V, MO, B, P, CO, NI, FE AND NABEING, PER MOL OF V, O.1 TO 0.95 MOL MO, 0.005 TO 0.3 MOL B, UP YO 0.5MOL P, UP TO 0.05 MOL CO, UP TO 0.05 MOL NI, UP TO 0.5 MOL FE AND UP TO0.6 MOL NA.
 2. A process as defined in claim 1, wherein said catalystcontains 0.01 to 0.5 mol phosphorus.
 3. A process as defined in claim 2,wherein said catalyst contains 0.02 to 0.6 mol sodium and 0.005 to 0.05mol of at least one member of the group consisting of cobalt, nickel andiron.
 4. In the vapor-phase oxidation of benzene to maleic anhydridewith molecular oxygen the improvement which comprises effecting suchoxidation in the presence of a molybdenum oxide-vanadium oxidephosphorusoxide catalyst wherein said molybdenum oxide, vanadium oxide andphosphorus oxide, expressed as Mo, V and P, are present per mol of V inthe amount of 0.1 to 0.95 mol Mo and 0.01 to 0.5 mol P, in combinationwith a small amount of boron oxide effective to prolong the active lifeof said catalyst.